M2 muscarinic receptors negatively modulate cell migration in human glioblastoma cells

Glioblastoma (GB) is a very aggressive human brain tumor. The high growth potential and invasiveness make this tumor surgically and pharmacologically untreatable. Our previous work demonstrated that the activation of the M2 muscarinic acetylcholine receptors (M2 mAChRs) inhibited cell proliferation and survival in GB cell lines and in the cancer stem cells derived from human biopsies. The aim of the present study was to investigate the ability of M2 mAChR to modulate cell migration in two different GB cell lines: U87 and U251. By wound healing assay and single cell migration analysis performed by time-lapse microscopy, we demonstrated the ability of M2 mAChRs to negatively modulate cell migration in U251 but not in the U87 cell line. In order to explain the different effects observed in the two cell lines we have evaluated the possible involvement of the intermediate conductance calcium-activated potassium (IK_Ca) channel. IK_Ca channel is present in the GB cells, and it has been demonstrated to modulate cell migration. Using the perforated patch-clamp technique we have found that selective activation of M2 mAChR significantly reduced functional density of the IK_Ca current in U251 but not in U87 cells. To understand whether the M2 mAChR mediated reduction of ion channel density in the U251 cell line was relevant for the cell migration impairment, we tested the effects of TRAM-34, a selective inhibitor of the IK_Ca channel, in wound healing assay. We found that it was able to markedly reduce U251 cell migration and significantly decrease the number of invadopodia-like structure formations. These results suggest that only in U251 cells the reduced cell migration M2 mAChR-mediated might involve, at least in part, the IK_Ca channel.